1. Field of the Invention
This invention relates to improvements in trucks for railroad locomotives and cars and, more particularly, to improved pedestal liners that form bearing surfaces for those portions of the trucks that are slidably engaged to accommodate relative movement, in a generally vertical direction, between the wheels and body of the locomotive car. More particularly, this invention relates to pedestal liners of the "floating" type in which the liners are not secured to the pedestals, but instead, are free to move in relationship to the pedestal leg.
2. Description of the Prior Art
The truck upon which a railroad locomotive or car body is supported is comprised essentially of two side frames tied together by a transverse piece called the "bolster." One type of truck commonly used for locomotives is referred to as a "pedestal truck." The pedestals are part of the side frames and are formed in inverted "U"-shaped sections that horizontally position and hold the journal box while permitting the journal box to move essentially vertically in relationship to the truck. The two projections that comprise the "U" of the pedestal are called the "pedestal legs" and the space between them the "jaw." The jaw is closed at the bottom when the journal box is inserted by means of a pedestal tie bar. In this arrangement, the journal box is held positioned in vertical sliding relationship with the truck and, since the locomotive body is supported by the bolster and side frames, vertical movement between the locomotive body and the journal box, journal and wheels is permitted.
As considerable wear takes place at the engaging faces of the pedestal and the journal box, it is common practice to attach wear plates to both the pedestal legs and the journal boxes. The former are referred to as "pedestal liners" and the latter as "journal box wear plates." Conventionally, the journal box wear plate is attached to the journal box by welding, whereas the pedestal liner is removably mounted as by bolting onto the pedestal legs.
Until recent years, the wear plates conventionally have been manufactured of hardened high-carbon spring steel or other alloy steel such as manganese steel. More recently, however, it has been found that improved performance can be obtained by utilizing wear plates made from some of the tougher plastics such as nylons, polyacetals, polyurethanes, polyolefins, polycarbonates, polyesters, rigid polyvinyls, polyethers, polysulfones, polyimides, polyamidimides, polysilcones, and the like. As is disclosed in U.S. Pat. No. 3,554,618, these plastic materials may be used to form a generally "U"-shaped wear plate that can be bolted onto the pedestal leg of a railroad truck.
Plastic pedestal liners particularly those made of nylon, have gained wide acceptance throughout the industry primarily due to the fact that they do not crack as frequently and so outwear alloy steel liners. Plastic liners are also advantageous in that they reduce the wear on mating surfaces such as the pedestal legs and the journal box and therefore reduce repair and maintenance of the railroad trucks.
While plastic pedestal liners have, by and large, proven considerably more satisfactory in use than the steel alloy liners, they do sometimes fail by cracking adjacent to those areas where they are bolted onto the pedestal. It is believed that under conditions of heavy use, the plastic liners can fracture due to the fatigue stress acting on liners through the point where they are secured to the pedestal leg. This stress cracking may become particularly pronounced under extremely cold winter conditions.
It has been conventional to bolt the pedestal liner to the pedestal leg and, indeed, it has always been thought necessary to do so, particularly with respect to steel pedestal liners. If the steel liners are not fastened to the pedestal leg, either by bolting or by welding, they may severely wear the mating cast steel pedestal legs, which then have to be rebuilt or replaced; they may hang up, resulting in damage both to the liners and the mating parts; they will pound against and cause fatigue to the journal boxes; and they cause excessive noise from metal surfaces impacting against each other.
In my copending patent application Ser. No. 708,661 filed on July 26, 1976, it is disclosed that, quite surprisingly, plastic pedestal liners do not have to be secured to the pedestal legs but may be permitted to "float"--i.e., move relative both to the journal box and the pedestal leg. By these means, the liners are not subject to the same fatigue stress and breakage as are other pedestal liners that are bolted on to the pedestal leg.
While plastic floating pedestal liners have proven quite satisfactory, unrestricted vertical movement of the liner may, under certain circumstances, cause damage to the liner and more than normal wear to the pedestal leg. First, if the pedestal liner is not restricted in vertical movement, it may work its way upwardly along the pedestal leg into a position where it can be severely impacted by the spring seat when the railroad car or locomotive goes over a bump in the rails. Second, rapid vertical movement of the pedestal liner, as sometimes experienced with high speed trains, may cause some wear to the surfaces of the pedestal leg.